The invention relates to a loading platform system for mounting on vehicle, particularly on trucks, comprising a platform lifting structure, an essentially plate-like loading platform for lifting and lowering loads and at least one lifting actuator mechanism for lifting and lowering the loading platform.
Such a loading platform system is described for example in EP-A-0 808 747. Loading platform systems of various designs have long been known. They are used particularly in connection with trucks in order to facilitate the lowering of loads carried by the truck from the truck loading bed to the ground on which the truck stands. From there, the load can be transported to its final destination by other means. The same is true for the loading of a truck. The load is first placed onto the loading platform while the loading platform is at ground level. The loading platform is then raised to the level of the loading bed of the truck and the load is then moved onto the loading bed.
In some designs of loading platform systems, the platform is pivoted, after completion of the unloading and loading procedure, from its horizontal position in which the loading and unloading occurs, to a vertical position for closing the rear access opening of the loading bed or a trunk-like loading space.
In other loading platform system designs, so-called folding loading platforms, the loading platform is not pivoted from a horizontal to a vertical position and vice versa. Rather, after the loading or, respectively, unloading procedure, the loading platform is folded and moved below the loading bed, that is, below the rear part of the loading bed of the truck.
For the raising and lowering of the loading board platform in an essentially horizontal orientation for the loading and unloading of a truck, a so-called lift actuator structure is used. Such an actuator structure is operated hydraulically, pneumatically, electrically or in another suitable way. For the pivoting of the loading platform from the vertical to a horizontal position and vice versa, that is, for the opening and closing of the loading bed space, a pivot actuator structure is used which operates hydraulically, pneumatically, electrically or in some other suitable way. Loading platform systems of the type referred to above therefore include at least two actuator structures. Generally, the lift actuator cooperates with one support structure for the loading platform whereas the pivot actuator cooperates with another loading platform support structure. The loading platform support structures may, but do not need to, include parallelogram type support lever arrangements. A loading platform pivot structure however isxe2x80x94as previously mentionedxe2x80x94only provided if the loading platform needs to be pivoted from a horizontal to a vertical position and vice versa.
It is known that, during loading and unloading, the raised loading platform, which then forms an extension of the loading bed of the truck, may be subjected to extremely high loads. For example fork lifts may be used for the loading and unloading procedure. In that case, the loading platform is not only subjected to the weight of the load but also the weight of the forklift used in the loading and unloading procedure.
The truck may be loaded or unloaded for example from the ramp of a warehouse while the loading platform is raised and disposed adjacent the ramp. A forklift carrying a load may then drive over the loading platform for loading the loads onto the truck bed or removing them therefrom.
In this way, the loading platform may be subjected to substantial loads, which increases the wear of the loading platform system. However, also from a safety point of view such loading of the loading platform is highly problematic since already partial failure of individual elements of the loading platform system may have fatal results for the persons performing the loading and unloading tasks. Also the loads being handled and the components of the loading platform system may be damaged upon failure of a component of the loading platform system.
It is the object of the present invention to provide a loading platform system of the type as described above, which is safely held in its raised position and wherein, in the raised position of the loading platform, the actuating structure remains free from stresses even when the loading platform is subjected to high loads. The system should furthermore be easy and inexpensive to manufacture and easy to handle during operation and wear of the actuating mechanism should be essentially eliminated while the loading platform is held in its raised position for loading and unloading.
In a loading platform system for mounting on a vehicle, especially a truck provided with a loading platform mounted to the vehicle by a lift support structure which is operated by a lift actuator for lifting and lowering loads onto, and from, a vehicle loading bed by way of the loading platform, means are provided for locking the loading platform in its raised position in which its surface is in planar alignment with the vehicle loading bed, thereby preventing exposure of the lift actuator to the stresses generated by heavy loads disposed on the loading platform during loading and unloading of the vehicle.
The arrangement according to the invention has the advantage, that with the loading platform locked in its raised position, for example fork lifts can drive onto and over the loading platform while the loading platform remains firmly positioned without transmitting the load to the lift support structure and the actuating mechanism. The arrangement is simple and can easily be retrofitted to existing loading platform systems. It may also be installed in newly manufactured loading platform systems, without the need for changes of the current design. The arrangement is furthermore inexpensive and simple to operate.
In a preferred embodiment concerning a loading platform system, in which the loading platform is pivotable from a horizontal to a vertical position for closing the load bed of the truck, the loading platform can also be locked in the vertical position. With the arrangement as shown in FIG. 2, the loading platform is safely locked in the vertical truck bed closing position so that it cannot be opened without disengaging the locking means. No stresses are transmitted to the actuating mechanism while the loading platform is locked in its vertical load bed closing position.
Basically only one locking means is needed to lock the loading platform in a particular position but two or more locking means may be used if it is expected that the loading platform will be subjected to large loads.
The locking means may be constructed in various ways. Preferably, the locking means includes a pin-like locking bolt, which is mounted on the vehicle and by which the loading platform is engaged or disengaged while the loading platform is raised and/or pivoted to a vertical position.
A pin-like locking bolt represents a simple embodiment as it requires merely a linear guide structure or bearing in which the bolt can be moved axially back and forth in order to engage or disengage an abutment structure on the loading platform.
The locking bolt can be engaged with, or disengaged from, the loading platform in any suitable way, for example, by electric motors or electromagnetic means. Preferably, however, the locking bolt is moved into, and held in, its engagement position by a pressure means, especially by a hydraulically or pneumatically operated piston and cylinder structure. A very simple pressure means is a compression spring.
If the loading platform is for example in a raised position at the same level as the loading bed of the truck and the pin-like locking bolt is in engagement with the locking structure on the loading platform, the loading platform could be unlocked manually. For example a handle may be provided which is connected to the locking bolt by a cable or a linkage for moving the locking bolt out of its locking position.
It is however particularly advantageous if the arrangement is such that the locking bolt can be moved to its unlocking position by initiating actuation of the lift actuator mechanism for lowering the loading platform. In this case, there is a coupling between the lowering that is the initiation of the lowering movement and the disengagement action of the locking bolt from the loading platform. This is possible for a system with a hydraulic, a pneumatic, electric, electric-motor or other kind of operating means. The same is true for the disengagement, which can be achieved by the source operating means. It is however also possible to use different power means for operating the lift actuator mechanism on one hand and the disengagement of the locking bolt from the loading platform on the other.
The engagement structure on the loading platform may comprise one or more sleevesxe2x80x94depending on the number of locking bolts usedxe2x80x94into which the locking bolts are inserted. However, because of the possibly high bending moments generated, upon loading of the loading platform, on the lifting and possibly also the tilting structure of the loading platform when it is locked in the raised position, the engagement structure of the loading platform preferably includes a roller element or, respectively, several roller elements under which the locking member or pin moves in the locking position. An elastic deformation of the loading platform when loaded while being locked and a slight pivoting because of the moment applied to the support structures will then not detrimentally affect the locking bolt as the roller elements permit slight movement of the bolt relative to the loading platform.
Below, an embodiment of the invention will be described in greater detail with reference to the accompanying schematic drawings.